It is known to produce controlled surface roughness in thin film magnetic recording disks in order to reduce motor starting torque relative to the rotation of the disks of a DASD unit. For example, this surface roughness is produced by a mechanical abrasive machining process, i.e. a material removal process, that textures the two planar and parallel surfaces of the disk upon which a thin film magnetic recording layer is subsequently deposited.
Generally speaking, the rigid disk shaped substrate member of a magnetic recording disk must be provided with smoothly polished, flat, surfaces in order to minimize magnetic recording layer defects, and in order to provide disk surfaces relative to which magnetic read/write heads can fly without damage occurring to either the disk or the head. However, if the disk is left with such an ultra smooth surface in the area of its start/stop track(s), the disk will likely present a high coefficient of static friction to the transducing heads.
Therefore, disk files which allow the head to come into static contact with the disk, for example in a head loading or start/stop area of the disk, generally provide a minimum level of roughness, at least at this area of the disk, in order to minimize the static friction thereof. This minimum roughness condition is currently achieved by abrasive machining, a process that results in material removal. As a result, a physical step tends to be provided between the disk's start/stop area and its data area.
A number of problems have been experienced with abrasive machine texturing. For example, small defects may occur in the disk surface, so as to interfere with head flying, or so as to cause data dropouts to occur. In addition, it is difficult to repetitively control the amount of abrasive machining that actually occurs during the texturing procedure. Cleaning of the disk substrate, after the abrasive texturing operation has been completed, is difficult to perform. Lastly, abrasive machine texturing is a relatively expensive procedure.
U.S. Pat. No. 4,326,229 describes another approach to solving this static friction problem in a magnetic recording disk for use in what is called a contact-start-stop (CSS) environment. In order to prevent adhesiveness of the disk surface, a protective layer is applied to the disk, this layer having jogs or undulations having a direction that extends transverse to the recording path, i.e. radially between the inner and outer circumference of the disk. These sinusoidal jogs are formed by surface tension that is exerted during spin coating of the protective layer.
In a preferred embodiment of the present invention an ultrasonic probe and a rigid disk substrate member, i.e. an aluminum disk, are placed in close proximity in a fluid abrasive slurry comprising a suspension of hard particles in a liquid. Energization of the probe thereafter operates to texture the substrate member, in the absence of removing material therefrom.
The use of an abrasive slurry to treat articles is generally known. U.S. Pat. Nos. 2,554,701, 3,698,408, 3,855,441 and 4,593,716 are examples.
The present invention improves the art of magnetic recording disks by providing a method and an apparatus for texturing the substrate member of a rigid magnetic recording disk, wherein the cost of the texturing process is reduced, wherein subsequent cleaning of the substrate member is simplified, wherein the texturing process is repeatable, and wherein head flying height and data dropout problems are minimized.